1. Field of the Invention
The present invention relates to methods for manufacturing droplet ejection heads, droplet ejection heads, and droplet ejection apparatuses. The present invention particularly relates to a method for manufacturing a droplet ejection head having high ejection performance with high yield, a droplet ejection head manufactured by the method, and a droplet ejection apparatus including the droplet ejection head.
2. Description of the Related Art
Inkjet recording apparatuses have many advantages: high-speed printing, low noise during printing, great freedom in the selection of ink, and the use of inexpensive plain paper. Among such inkjet recording apparatuses, the following apparatus has recently become mainstream: an ink-on-demand type inkjet recording apparatus for ejecting ink droplets only during printing. This type of inkjet recording apparatus has an advantage that the collection of unnecessary ink droplets is not necessary.
Examples of the ink-on-demand type inkjet recording apparatus include an electrostatic inkjet recording apparatus for ejecting ink droplets using static electricity, a piezoelectric inkjet recording apparatus including a piezo-element for driving, and a bubble jet® type inkjet recording apparatus including a heating element.
In these inkjet recording apparatuses, ink droplets are ejected from nozzles of inkjet heads. Arrangements of the nozzles are classified into two types: a side ejection type in which ink droplets are ejected from a side face of an inkjet head and a face ejection type in which ink droplets are ejected from the front face of an inkjet head.
In an inkjet head of the face ejection type, the thickness of a nozzle substrate is preferably adjusted by adjusting the flow resistance in nozzle channels such that nozzles have an optimum length.
Japanese Unexamined Patent Application Publication No. 9-57981 (hereinafter referred to as Patent Document 1) discloses a method for manufacturing a nozzle plate for known face ejection-type inkjet heads. In the method, after a silicon substrate is ground so as to have a desired thickness, first nozzle channels and second nozzle channels connected thereto are formed in the silicon substrate by etching both faces of the silicon substrate.
Japanese Unexamined Patent Application Publication No. 11-28820 (hereinafter referred to as Patent Document 2) discloses a method for forming nozzles for known face ejection-type ejectors (droplet ejection heads). In this method, first nozzle channels and second nozzle channels, connected thereto, having a diameter different from that of the first nozzle channels are formed in a first face of a silicon substrate by anisotropic dry etching using ICP discharge and a second face of the silicon substrate that is opposite to the first face thereof is then processed by anisotropic wet etching, whereby the length of the nozzles are adjusted.
In the method disclosed in Patent Document 1,there is a problem in that since the silicon substrate is ground so as to be reduced in thickness before the formation of the first and second nozzle channels by dry etching, the silicon substrate is cracked or chipped during manufacturing steps. This leads to a reduction in yield, resulting in an increase in manufacturing cost.
Furthermore, in this method, there is a problem in that since a face of the nozzle plate that is opposite to a processed face thereof is cooled using a helium gas or another gas during dry etching such that the nozzle plate can be accurately processed, the helium gas flows to the processed face from the opposite face at the point of time when any nozzle penetrates the nozzle plate, whereby etching is prevented.
In general, the inner walls of nozzles must be covered with ink-resistant protective layers made of silicon dioxide. However, in this method, there is a problem in that since the silicon substrate has a small thickness and is therefore readily distorted due to its weight, the silicon substrate cannot be set in a thermal oxidation system for forming an ink-resistant protective layer by thermal oxidation. Furthermore, if the ink-resistant protective layer is formed by chemical vapor deposition (CVD) or sputtering, in which the heat load is low, instead of thermal oxidation, the ink-resistant protective layer cannot be uniformly formed over the walls of the nozzles.
In the method disclosed in Patent Document 2,there is a problem in that since an ejection face in which openings of the first nozzle channels are arranged is located back from the front face of the substrate, droplets fly in curved paths. Furthermore, there is a problem in that the following operation cannot be readily performed due to its configuration: a wiping operation for removing paper or ink dust, which causes nozzle plugging from the ejection face with a piece of rubber or felt.